Restriction of recombination in particular chromosomes of Drosophila melanogaster has been shown to reduce the effectiveness of selection for positive and negative geotactic and phototactic behavior. The results reflect an underlying organization of the genes controlling these two behaviors in this species. Genetic analysis of phototaxis and geotaxis in other species of Drossphila will reveal any existing relationships between genetic homologies and evolutionary distance. Several correlated responses to selection for geotactic behavior have been observed. Geopositive flies mate much more rapidly than geonegative flies do. Drosophila melanogaster females from geopositive and geonegative strains show differences in their utilization of oviposition sites when given a choice of upper and lower egg laying surfaces. Correlated responses to selection have also been observed in phototactic strains of D. melanogaster. Females from photopositve strains lay twice as many eggs in the light than they do in darkness and females from the photonegative strain lay more eggs in the dark than in light. Experiments using recessive eye color mutants have shown that alterations of screening pigment composition will affect normal phototactic behavior. Various ERG defective mutants are being employed to examine the effects of lesions in the visual pathway on behavior in the phototaxis maze.